Optimize the message queue for many active ports with few messages.

runtime/vm/dart_entry.h

Index: runtime/vm/dart_entry.h
diff --git a/runtime/vm/dart_entry.h b/runtime/vm/dart_entry.h
index 8a4c540cd0795c8bc73a4ce894f3114c64dc2d2a..dcf3a34182a903d08c0c0ac6bf97c26d48af40ba 100644
--- a/runtime/vm/dart_entry.h
+++ b/runtime/vm/dart_entry.h
@@ -153,8 +153,12 @@ class DartLibraryCalls : public AllStatic {
   // On success, returns a RawInstance.  On failure, a RawError.
   static RawObject* Equals(const Instance& left, const Instance& right);
 
+  // Returns the receive port if it is in the port map and null otherwise.
+  // On failure, a RawError.
+  static RawObject* LookupReceivePort(Dart_Port port_id);
+
   // Returns null on success, a RawError on failure.
-  static RawObject* HandleMessage(Dart_Port dest_port_id,
+  static RawObject* HandleMessage(const Object& receive_port,
                                   Dart_Port reply_port_id,
                                   const Instance& dart_message);